(Btw, if you haven't checked out globalpost.com yet, do it!)
This article (which includes an awesome poster gallery) discusses the trend-turned-cultural-value of having only one child in South Korea. It grew out of population control campaigns in previous decades and the high cost of raising and educating a child.
The only trouble is, now Koreans aren't having enough babies. (Yeah, crazy.)
When I lived there, I taught at a school run by Mormons, so I actually saw a lot of two- three- four- and even five-child families. That was, of course, the exception. I also observed that my students were totally up on contraception methods and sex-ed (I taught Health Class), at least in theory. In practice they would have seemed years behind American high schoolers.
One thing I also found interesting was that in Korea you can get the birth control pill over the country at pretty much any pharmacy. That is, again, leftover from population control days.
Just another example of how terms like "conservative" and "liberal" when it comes to social values are totally subjective. Things that seem contradictory to Americans aren't contradictory when you look at them in a different cultural context.